This invention relates to pneumatic vehicle tires and wheel rim assemblies and in particular insuring greater vehicle safety by a method and device for preventing the mounting of a tire on a wheel rim of a size and type that is not intended to receive that tire. Each tire of a particular size and type is designed to be mounted upon a particular size wheel rim. The variables in tire to wheel rim fitment include rim bead seating diameter verses tire bead diameter; axial design width (distance between the two beads) of the tire verses axial width of the wheel rim and the bead seating angle. All of these variables must be compatible to have a proper fitment of the tire on the wheel rim.
The presently popular pneumatic vehicle tire is well known, it has a toroidal shaped elastomer carcass with at least one carcass reinforcing ply embedded therein and a tread band on its outer ground contacting surface. The radial inner ends of the carcass ply are turned up around a pair of bead wires or bead bundles, which are usually made of a plurality of steel wires. The bead bundle is normally of planar circular configuration but it can be forcedly distorted into an oval and into a non-planar shape for the purpose of mounting on a one piece steel wheel rim. In ordinary use the bead bundle is considered to be "inextensible" but this is of course a relative term and if subjected to too much stress, the bead bundle can stretch or break.
The wheel rim, when viewed in cross section along a radial plane extending parallel to the axis of rotation of the tire, has a pair of radially outwardly extending flanges on the axially outer sides of the wheel rim and axially inward from each flange is a bead seating surface and central portion of smaller diameter in the form of a drop center portion or well. This well has a diameter smaller than the bead seating surface diameter so that when a tire bead is forcedly distorted so as to pass over the wheel rim flanges, the portion of the tire bead passed over the flanges can then be dropped into the well so that the diametrically opposite portion of the tire bead can then also be forced over the wheel rim flange. Thus the entire circumference of both tire beads may be passed over the flanges, step by step working around the bead circumference, until both beads are in the well. In modern day passenger car and light truck tires there is usually no inner tube in the tire but instead a tire inflation valve is mounted in an aperture in the wheel rim. Heavy truck and bus tires may have an inner tube although the trend is toward tubeless tires. If there is a tube the inflation valve is of course part of the tube. Upon pressurizing the inside of the tire, by use of the tire valve, the tire beads will be forced axially outward so as to seat, with an interference fit, snugly upon the wheel rim bead seating surfaces and pressed axially outward against the rim flanges.
The radial inward end of the bead is an annular surface which, when properly seated on the rim bead seating surface, lies at an angle to the axial direction; in passenger car tires this angle is 5.degree.; in tubeless truck and bus tires it is 15.degree.. However in light truck tires both 5.degree. and 15.degree. seating angles exist; this is part of the problem of mismatched mounting of tires and wheels.
When the tire beads are properly seated on a wheel rim for which they are designed to be mounted the bead core wires will be stretched tight and due to the taper of the bead seating surface, the surrounding relatively hard rubber, the inflation pressure and compression of rubber and fabric under the bead, the bead will stay firmly in place when the tire is subjected to strong sideway forces during turning, accident avoidance maneuvers, acceleration and deceleration of the vehicle, thus enabling the driver to get and keep the vehicle under proper control.
When the tire beads are not properly mounted, especially when a tire is placed upon a wheel rim for which it was not intended, e.g. a tire bead diameter of 16 inches on a bead seating surface of 16.5 inches, disastrous results can follow. This includes: breaking of the bead core wires so that the tire blows off the rim when inflated; breaking, kinking or displacement of some of the wires of the bead bundle so as to make the tire susceptible to early failure; stretching of the bead bundle so as to lead to an improper fit that will impair the tire's structural integrity.
The sideway force on a tire tends to exert a force on the bead of that tire tending to cause the bead bundle to rotate about its own longitudinal axis with the hard rubber filler strip that is radially outward of the bead bundle acting as a lever arm to cause the bead to rotate about the bead bundle on the rim bead seating surface. If the bead does succeed in rotating, the bead will usually become of a different effective circumference, upsetting the tension on the reinforcing bead bundle wires, and permitting at least one of the tire beads to unseat, that is to move axially inwardly toward the center of the rim and into the well. If this happens, the driver's control very likely will be lost.
In the prior art in passenger car tires the possibility of mounting the wrong size tire on a wheel rim had been largely avoided by making a distinct difference in sizes; e.g. maintaining at least a whole inch diameter difference between sizes. Thus popular tire bead diameter sizes have in the past been 13 inch, 14 inch, 15 inch, 16 inch, 17 inch, etc. with a 5.degree. taper but not any 131/2, 141/2, 151/2 or 161/2 inch sizes or 15.degree. tapers in passenger car tires. Maintaining at least a whole inch difference between size can prevent tire rim mis-mountings; for example, it is virtually impossible to get a 13 inch tire over the rim flanges of a 14 wheel and if one could do so, upon attempt to inflate the tire to seat the flanges, the 13 inch tire bead diameter will simply not fit onto the bead seating surface of a 14 inch wheel rim. This lack of fit is caused by two factors: the difference in diameter and the fact both the wheel rim and the tire are 5.degree. tapers which is relatively "flat" with little opportunity for an improper size to even get started on the bead seating surface even when considerable air pressure for mounting is applied.
Experience has shown that a 16 inch 5.degree. tire can be introduced onto a 16.5 inch 15.degree. wheel rim and that such an introduction will not result in a proper mounting even if it might appear visually to be correct. Unfortunately the relative diameters and the 15.degree. seating surface on the wheel rim will lead to a situation where the inflation pressure (especially high inflation pressure) will cause a seal (albeit an improper seal) between the tire beads and the rim that is usually sufficient for the tire to inflate and thus potentially misleading the tire installer to believe that the tire is a proper fit on the wheel rim when such is not in fact the case. In such a mounting the tire beads are not properly engaged with the rim so that the entire radially inwardly facing annular surface of the tire bead is no likely to be in full intended contact with the wheel rim bead seating surface, thus setting up a situation for latent failure (i.e. bead breakage or other bead area damage).